1. Field of the Invention
The present invention generally relates to SAR/ISAR imaging systems and, more particularly, is concerned with a method of correcting rotational motion error in SAR and ISAR imagery to increase focus and clarity of radar images.
2. Description of the Prior Art
In synthetic aperture radar (SAR) and inverse synthetic aperture radar (ISAR) systems, the radar signal processing equipment operates on a basic assumption that the relative motion between the radar and the target being imaged is in a straight line at a constant speed. In the real world, the relative motion is subject to deviations due to many causes and it is therefore necessary to provide compensation for these perturbations
Rotational motion error terms occur in synthetic aperture radar (SAR) and inverse synthetic aperture radar (ISAR) imagery when the relative viewing angle between the radar and the target to be imaged, deviates from being linear throughout the imaging integration time. These error terms can cause significant image blurring. The problem to be resolved is to estimate and remove phase error terms which are caused by the unwanted rotational motion perturbations in the real SAR and ISAR imagery, thereby focusing the image.
In both SAR and ISAR imaging, the cross range information is obtained by interrogating the target at constant increments in viewing angle change between the target and the radar over a certain time period. In ISAR the target rotates relative to the stationary radar, whereas in SAR the radar moves in an arc to provide the viewing angle change. If the rotation rate deviates from being constant during the imaging time in either case, there will be phase errors in the image data and the imagery will be blurred.
Consequently, a need exists for a way to resolve the aforementioned problem of rotational motion error occurring in both SAR and ISAR imagery in order to reduce image blurring and improve image clarity.